Mercury-cathode rectifier



P 3 J. G. w. MULDER 2,173,023

MERCURYCATHODE RECTIFIER I Filed March 17, 1937 JG wmuzazez" PatentedSept. 12, 1939 UNITED STATES PATENT OFFICE MEROURY- CATHODE RECTIFIERApplication March 17, 1937, Serial No. 131,491 In Germany March 20, 19367 Claims.

My invention relates to single-phase mercurycathode rectifiersparticularly those of the type described in my copending U. S. patentapplication Ser. No. 67,155, filed March 4, 1936, now

5 Patent #2,170,482.

Such rectifiers comprise an envelope having a cup-shaped metal portionand a glass portion hermetically fused together, a mercury cathode inthe bottom of the metal portion, which portion 10 may be artificiallycooled, and a main anode arranged parallel with the axis of the envelopeand above the surface of the mercury cathode. To obtain a compactconstruction the main anode is disposed at a comparatively shortdistance from 15 the mercury cathode, and as there is a direct dischargepath between the anode and the cathode, there is considerable danger ofarcing back at high A. C. voltages. More particularly, in such tubes theliquid mercury is vigorously 2() splashed from the mercury surface bythe motion of the cathode spot thereon and by the highlycompressedmercury vapor formed in the vicinity thereof, and may readily strike theanode and .cause arcing back particularly at high anode 5 voltages,

In accordance with the present invention I overcome the abovedifiiculties by providing in the discharge space between the main anodeand the surface of the mercury cathode, partitioning 30 means whichintercept straight lines between any point on the active cathode areaand any point on the main anode while allowing for the passage of thedischarge.

Such partitioning means prevent the liquid mercury particles, or thehigh-pressure mercury vapor issuing from the cathode, from directlyreaching the anode by insuring that these particles deposit on othercolder portions of the tube and that locally-limited rises of the 40mercury vapor pressure are smoothed out before reaching the anodesurface.

By the term the active cathode area as used herein and in the claims ismeant that part of the mercury cathode surface which can be cov- =45ered by the cathode spot of the discharge. Thus parts of the surfaceoutside the area defined by limiting bodies placed in the cathodemercury would not form part of the active cathode area.

In one embodiment of my invention I provide ,5 in the discharge space ofthe rectifier, a labyrinth-like structure comprising a plurality ofpartitioning or barrier members alternately projecting from oppositedirections into the dis- :charge path, whereby the discharge space-as 55viewed in the direction cathode-anodeappears to be covered in anoverlapping manner over its entire cross section and a curved path isleft free for the discharge between the anode and the cathode. Byincreasing the number of partitioning members-depending upon the valueof the anode vo1tagethe labyrinth effect of the structure can beincreased accordingly. The number of partitioning members used islimited only by the resulting increase in the voltage drop of thedischarge, and by the ignition difiiculties. 10

As such a multi-labyrinth structure may introduce ignition difliculties,I overcome this difilculty by making one or more of the members ofconductive material, electrically insulate same from the other parts ofthe tube, and apply thereto a desired potentiaL. Thus the individualpartition.- ing members can be given suitable potentials in a mannerknown per se, whereby the ignition of the discharge occurs in steps fromthe cathode to succeeding partitioning members.

To improve the functioning of the partitioning members, I increase thecondensation effect thereof by securing at least one of the members ingood heat-transferring relationship to an artificially-cooled memberprojecting into the discharge space. Such a cooling member may axiallytransverse the anode or the mercury cathode in a manner known per se andproject into the discharge space from above or below.

Further features and advantages of my invention will appear as thedescription progresses.

In order that my invention may be clearly understood and readily carriedinto effect, I shall describe same more fully with reference to theaccompanying drawing, in which: 5

Figure 1 is a sectionized sideview of a rectifier embodying theinvention; and

Fig. 2 is sectionized side-view of a rectifier according to anotherembodiment of the invention.

The rectifier shown in Fig. 1 has an envelope comprising a cup-shapedmetal portion I, for instance of chrome iron, to which is hermeticallyfused at IS a vitreous portion 2. I-Iermetically sealed in portion 2 isa metal disc in carrying a terminal 5, and a conductive rod II to thelower end of which is secured a cylindrically-shaped" main cathode 1.Rod 1| serves as a supply conductor for anode I and is surrounded by atube 5! of insulating material, for instance steatite.

Supported from tube 5| is a cylindrical shield I4, for instance ofmolybdenum plate, closed at its top and serving to protect seal l5 fromthe detrimental effect of the discharge in the manner described in myabove-mentioned patent. Supported from shield 14 by suitable clamps andeX- tending through a groove in the periphery of anode l is a guide tube9 of insulating material, for instance steatite. A conductive rod 8 isslidably disposed within the bore of tube 9 and carries on its lower endan ignition anode 4, and on its upper end an iron plunger l0.

Plunger I3 is electrically connected through a compression spring H toan iron core I2 supported by a conductive rod 6 from a disc hermeticallysealed in the upper end of a protruding part of portion i. A coil 13having one lead connected to rod 6 surrounds glass portion 1 in thevicinity of core l2 and serves to move the assembly consisting ofplunger l0, rod 8 and anode in a vertical direction to thereby liftanode 4 from a mercury cathode disposed at the bottom of portion I.

To restrict the free movement of mercury 2, concentrical rings H and 18,for instance of molybdenum, are secured, for instance welded, to thebottom of portion I and extend slightly from the surface of the mercury.

Disposed at the center of mercury 3 and extending slightly above thesurface thereof, is a cylindrical metal member I5, whichserves to anchorthe cathode spot in known manner. Member i6 is preferably formed of ametal which has a higher dissolving speed in mercury than does copperand which amalgamates better than does iron or molybdenum, for instancenickel. Anchoring members of this type have been described in detail inthe copending U. S. patent application Ser No. 125,943 to Jurriaanse,now Patent #1118387.

Metal portion 1 is artificially cooled, and for this purpose issurrounded by a cooling jacket 20 provided with an inlet opening 2| andan outlet opening 22 for the circulation of a suitable cooling mediumsuch as water or oil. Jacket 20 is secured to the bottom of portion 1 bya suitable bolt i9 also serving as a supply conductor for cathode 3,whereas a ring-shaped member closes the top thereof.

In accordance with the invention, partitioning means are provided in thedischarge path between anode l and cathode 3 to prevent back discharge.For this purpose a ring 23, for instance of molybdenum, and having anaperture 54 is supported from and in direct metallic contact withportion l-for instance by having its periphery welded thereto-whereas adisc 23 of conductive material, for instance of molybdenum and of largerdiameter than aperture 54 is fixedly supported from insulating tube 9 soas to extend normally to the axis of main anode T and substantiallycoaxially therewith. Due to these partitioning means the discharge mustpass, as indicated by the arrows 52 through aperture 54, and isdeflected by disc 23 to pass over the artificially cooled wall ofportion I before reaching the lower surface of anode 1. As ring 23 is indirect metallic contact with the artificially-cooled wall of portion i,it is maintained at a relatively low temperature whereby thecondensation of the mercury vapor therein is increased.

It should be noted that the disc 24 and ring 23, or a plurality of suchdiscs and rings, form a labyrinth-like structure, and that a straightline between any point on the anode and any point of the active surfacearea of the cathode 3 is intercepted by either ring 23 or by disc 24.

To facilitate ignition of the tube, a given potential may be applied tothe disc 24, and for this purpose a supply lead 53 is provided which isconnected to a terminal 66 led through the vessel wall by means of themetal disc 61. Thus disc 24 may also have the functions of a controlgrid. For ignition purposes disc 23 may be given a positive voltage ofthe order of volts.

If it is desired to make the arrangement more eificient, a larger numberof alternately-arranged members, similar to disc 23 and ring 23, may beused, and by making the outer diameter of the discs greater than thediameter of the apertures in the rings the discharge path between thecathode and anode will have several curves. In such a constructionseveral of the partitioning members can be given suitable potentials sothat the ignition of the discharge takes place in steps from the cathodeto succeeding partitioning members. In such cases it is advisable topre-connect series-resistances of suitable values to limit the current.

The rectifier shown in Fig. 2 has an envelope comprising a cup-shapedmetal member 39 and a ring-shaped metal member 2'? secured together by avitreous ring 38 sealed to members 39 and 21 at 55 and 56, respectively,and a vitreous portion 29 fused to the upper edge of member 27 at 5T.

Secured to a threaded projecting portion of member 2T is a main anode 25provided with a central bore 58 and an eccentric bore 59. A suitable1ug'28 secured to member 21 serves as a supply terminal for anode 26.

Sealed in the upper portion of member 29 is a disc 63 provided with aterminal 33. Secured to the lower surface of disc 65 and extendingthrough aperture 59 is a conductive rod 6| carrying on its lower end anignition member 3i, or igniter, consisting of a semi-conductive materialsuch as silicon carbide. An insulating tube 32 surrounds rod tl and issupported by member 3 I.

Sealed to member29 at 62 isa tubular member 33 having an outlet opening3", and an inlet opening 35 in the form of a tube extending almost tothe bottom of member 33. Member 33 is provided with a terminal 34 andextends through aperture 58 into the discharge space with a clearance soas to be insulated from anode'2ii. A suitable circulating liquidfSi, forinstance water or oil, is circulated in the direction of the arrows tocool member 33.

Disposed in the bottom of metal portion 39 is a mercury cathode lflfandconcentric rings 43 and 50 which, similar to rings l8 and IQ of Fig. I,prevent free movement of the mercury.

A cooling jacket 42 having an outlet opening 43 surrounds member 39 andis secured thereto by a hollow bolt 3| having an inlet opening 44 andtwo outletopenings G5. Jacket 42 is closed at its upper end by a metalmember 5 3 welded to member 39 andscrewed to the top edge of coolingjacket 42.

An annular cathode spot anchoring member 38, for instance of nickel, issecured to the upper portion of bolt 4| and to member 39, for instanceby being welded thereto. Bolt M is provided on its lower end with anexternal thread cooperating with suitable nuts to form'a liquid-tightseal at the point of support of jacket 32. A terminal 33 secured to bolt4|, serves as a supply terminal for cathode 40.

As indicated by arrows, a suitable circulating cooling fluid such aswater or oil passes through opening 34, through the hollow of bolt 4|,through openings 45, and, after passing through cooling jacket 42,leaves through the outlet opening 43.

According to the invention the discharge path between anode 26 andcathode 40 is intercepted at several points. For this purpose a .ring 41having an aperture 65 is peripherally secured to member 39, for instanceby welding, and members 31 and 46 of conductive material and having alarger diameter than aperture .65 are secured, for instance welded, tomembers 33 and 4| respectively. Thus members 31 and 46 are maintained ata desired low temperature by means of the circulating cooling fluidflowing through in members 33 and 4| respectively, whereas member 41 isalso maintained at a low temperature by being directly connected to thecooled wall of member 39. Furthermore the fiow of cooling liquid throughmember 4| insures an even cooling in the immediate vicinity of the footpoint of the discharge.

The terminal 34 may be used in conjunction with disc 3! as a controlmember for influencing the passage of the discharge through the tube,and for this purpose it is important to thoroughly insulate member 33from anode 26.

Thus a construction such as shown in Fig. 2 has the advantage that theanode, the mercury cathode, and the discharge space between these twoelectrodes are subjected to a supplementary cooling whereby still largerquantities of energy can be taken up inside the very compact dischargespace or, conversely, the voltage drop in the arc and the correspondinglosses can be reduced. In either case the security against arcing backof the tube is materially increased. With such a construction it ispossible even at high anode voltages, for instance 500 volts A. C. andmore, to accurately rectify currents of considerable intensity forinstance of several hundred amperes.

Furthermore the problem of providing an insulated current supply leadfor a partitioning member acting as a control grid is solved in a simplemanner by using the cooling member 33 for this purpose.

While I have described my invention in connection with specific examplesand applications, I do not wish to be limited thereto but desire theappended claims to be construed as broadly as permissible in view of theprior art.

What I claim is:

1. A single-phase mercury-cathode rectifier comprising an envelopehaving a cylindrical cupshaped metal portion and a glass portionhermetically sealed to the edge of said metal portion, a mercury cathodein said metal portion, an anode axially disposed in the envelope andspaced from said cathode, partitioning means forming a circuitousdischarge path between said anode and cathode and intercepting astraight line between any point on said anode and any point on theactive cathode area, said means comprising an annular partitioningmember snugly fitting into said metal portion and secured thereto, and apartitioning member of conductive material supported from said glassportion and insulated from the other portions of the rectifier, andmeans for applying a potential to said member.

2. A single-phase mercurycathode rectifier comprising an envelope havinga cup-shaped metal portion and a glass portion hermetically fusedtogether, a mercury cathode in said metal portion, a main anode ofslightly smaller cross section than the metal portion and provided witha bore, said anode being supported from said glass portion and lyingpartly within said metal portion, a member supported from said glassportion and extending through said bore, and means to form a circuitousdischarge path between said anode and cathode and intercepting astraight line between any point on said anode and any point on saidcathode, said means comprising an annular plate snugly fitting into saidmetal portion and secured at its edge to the surface thereof, and a disccarried by said member.

3. A single-phase mercury-cathode rectifier comprising an envelopehaving a cup-shaped metallic bottom portion and a vitreous upper portionhermetically sealed together at the periphcry of the tube, a mercurycathode in the bottom of said cup-shaped portion and in direct metalliccontact therewith, a main anode axially disposed in said envelope andextending into the space enclosed by said vitreous portion, said anodebeing spaced from said cathode to form a discharge path, partitioningmeans between said anode and cathode and intercepting a straight linebetween any point on the anode and any point on the active cathode areawhile allowing for the passage of a discharge between said anode andcathode, said means comprising a metal barrier secured with a metallicconnection at its periphery to said metallic bottom portion to ensuregood transfer of heat, and means to artificially cool said metallicbottom portion and said metal barrier.

4. A single-phase mercury-cathode rectifier comprising an envelopehaving a cup-shaped metallic bottom portion and a vitreous upper portionhermetically sealed together at the periphery of the tube, a mercurycathode in the bottom of said cup-shaped portion and in direct metalliccontact therewith, a main anode axially disposed in said envelope andextending into the space within said vitreous portion, said anode beingspaced from said cathode to form a discharge path, partitioning meansbetween said anode and cathode intercepting a straight line between anypoint on the anode and any point on the active cathode area whileallowing for the passage of a discharge between said anode and cathode,said means comprising a metal ring secured with a metallic connection atits periphery to said metallic bottom portion to ensure good transfer ofheat, and a metal disc, a member supported from said vitreous portionand carrying said disc, and means to artificially cool said metallicbottom portion and said ring.

5. A single-phase mercury-cathode rectifier comprising an envelopehaving a cup-shaped metallic bottom portion and a vitreous upper portionhermetically sealed together at the periphery of the tube, a mercurycathode in the bottom of said cup-shaped portion and in direct metalliccontact therewith, a main anode axially disposed in said envelope andextending into the space within said vitreous portion, said anode beingspaced from said cathode to form a discharge path, partitioning meansbetween said anode and cathode and intercepting a straight line betweenany point on the anode and any point on the active cathode area whileallowing for the passage of a discharge between said anode and cathode,said means comprising a metal barrier secured with a metallic connectionat its periphery to said metallic bottom portion to ensure good transferof heat, and a metal member, means to artificially cool said metallicbottom portion and said barrier, and means for cooling said metal memberincluding a memher extending through the discharge space of'the tube.

6. A single-phase mercury-cathode rectifier comprising an envelopehaving a cup-shaped metallic bottom portion and a vitreous upper portionhermetically sealed together at the periphery of the tube, a mercurycathode in the bottom of said cup-shaped portion and in direct metalliccontact therewith, a main anode axially disposed in said envelope 2ndextending into the space within said vitreous portion, said anode havinga bore and being spaced from said cathode to form a discharge path,partitioning means between said anode and cathode and intercepting astraight line between any point on the anode and any point on the activecathode area while allowing for the passage of a discharge between saidanode and cathode, said means comprising a metal barrier secured with ametallic connection at its periphery to said metallic bottom portion toensure good transfer of heat, and a second metal barrier, means to coolsaid second metal barrier including a member passing through the bore insaid anode, and means to artificially cool said metallic bottom portionand said first metal barrier.

7. A singlephase mercury-cathode rectifier comprising an envelope havinga cup-shaped metallic bottom portion and a vitreous upper portionhermetically sealed together at the periphery of the tube, a mercurycathode in the bottom of said cup-shaped portion and in direct metalliccontact therewith, a main anode axially disposed in said envelope andextending into the space within said vitreous portion, said anode beingspaced from said cathode to form a discharge path, partitioning meansbetween said anode and cathode and intercepting a straight line betweenany point on the anode and any point on the active cathode area whileallowing for the passage of a discharge between said anode and cathode,said means comprising a metal barrier secured with a metallic connectionat its periphery to said metallic bottom portion to ensure good transferof heat, and a second metal barrier, means to cool said second barrierincluding a member extending through the mercury cathode, and means toartificially cool said metallic bottom portion and said first barrier.

JOHANNES GIJSBERTUS 'VVILHELM MULDER.

